A wide variety of fluid delivery devices have been developed for various applications, such as the delivery of medicine or drugs. By way of example, automated infusion devices that can deliver a fluidized or fluid-borne drug to a subject with extremely high precision have been developed. (See, for example, the above-referenced U.S. Patent Application Publication No. 2004/0115067 A1 and the above-referenced U.S. Patent Application Publication No. 2005/0238503 A1 of Benjamin Rush et al, concurrently filed herewith.) If these devices fail to deliver a drug to a subject at an acceptable or intended rate, the consequences can be anywhere from relatively minor to relatively major, even deadly. Thus, some means of verifying that a drug is being delivered or has been delivered at an acceptable or intended rate is typically incorporated into automated drug infusion devices.
Drug delivery verification means may allow for the detection of insufficient and/or excessive drug delivery or fluid flow. Traditional means or methods for measuring fluid flow include hot-wire anemometry, generation and detection of a heat pulse, injection and detection of a tracer component, and electromagnetic flow measurement, such as via passage of an ion-containing liquid through a loop and detection of an associated current.
Other means for measuring fluid flow have been developed for specific devices, as well. For example, means for detecting a build-up of pressure within a drug delivery path, such as that caused by a blockage in the path, have been incorporated into portable insulin pumps. These means, which include a pressure transducer, can detect insufficient fluid flow from the insulin pump, such as insufficient flow caused by a blockage in the delivery tubing or in the cannula, but cannot detect excessive fluid flow from the pump. The pressure transducer adds to the cost and complexity of this portable insulin pump.
Another method of detecting insufficient fluid flow from a fluid delivery device, such as a drug delivery device, has been disclosed. (See U.S. Pat. No. 6,692,457.) According to this method, the fluid flows past a resilient chamber, such as a balloon or a bubble, in the flow path. If the flow path is blocked at a point downstream from the bubble, for example, the pressure in the flow path increases, such that the bubble expands and a surface of the expanded bubble activates a sensor to indicate a blockage condition.
Methods of monitoring the rate of fluid delivery from a drug delivery device have also been disclosed. (See U.S. Pat. No. 6,582,393 and U.S. Patent Application Publication No. 2004/0019321 A1.) According to one such method, a small amount of fluid is heated via a heating element, such as a laser, and the presence of this heated amount of fluid is detected downstream via a heat sensor, such as another laser, and a rate of fluid flow is determined and evaluated. According to another such method, the flowing fluid is subjected to a magnetic field, such that ions in the fluid produce a directional current, which is then detected and associated with the volumetric flow rate. Compensating adjustments to the flow rate may then be made accordingly.
Devices for measuring fluid flow have also been developed for applications unrelated to drug delivery. By way of example, a device for measuring the very slow flow associated with hydrothermal systems, such as hydrothermal systems on the seafloor or dilute hydrothermal systems, has been described at http://gore.ocean.washington.edu/ research/slow_flow_meter.html. In the case of seawater, the seawater fluid enters the tubular device and generates a “puff” of chlorine gas at a platinum electrode of an electrode pair within the device, via the electrochemical reaction, 2Cl−→Cl2+2e31 . The puff is confined within the device, where it is detected via two sensing electrodes placed at fixed distances from the platinum electrode along the tubular device. The times required for the puff to travel known distances along the device provide a measure of the flow velocity of the seawater.
Devices for measuring various parameters of a moving fluid have also been developed for various applications. By way of example, a rotating disk electrode has been developed as a means of producing a very regular and reproducible liquid flow profile when immersed in a liquid. If the liquid contains a dilute species that can react at the electrode, the rate of reaction will depend on the speed of rotation associated with the rotating disk electrode. This phenomenon may be used to determine the concentration of the dilute species in the liquid. (See, for example, A. J. Bard and L. R. Faulkner, Electrochemical Methods, 2nd Ed., John Wiley (2001).)
Further development of fluid flow measurement devices, and associated systems, devices and methods, is desirable.